Integrated multiaxial articles have wide applications such as advanced composites, power transmission and conveyer belts, fabrics in paper forming machines, among others.
Advanced composites include high performance fibers in a matrix. Depending on the fibers, matrix materials and manufacturing parameters, advanced composites offer superior strength-to-weight and modulus-to-weight ratios, fatigue strength, damage tolerance, tailored coefficient of thermal expansion, chemical resistance, weatherability, temperature resistance, among others.
Fibers are the basic load-bearing component in a fiber reinforced composite. They are often pre-assembled into various forms to facilitate the fabrication of composite parts. Advanced composites are often made from prepreg tapes, sheets and fabrics that are parallel continuous fibers or single-layer fabrics held by a matrix forming material. They are used to make parts by laminate layup and tape or filament winding. The traditional laminated composites are vulnerable to delamination because the layers of strong fibers are connected only by the matrix material that often is much weaker than the fibers. Integrated fiber structures with the introduction of fiber reinforcement in the through-the-thickness direction could effectively control delamination failures and make the composite very damage tolerant. Besides performance enhancement, composites reinforced with integrated fiber structures may also offer other advantages such as high level of automation, high production rates, reproducibility, flexibility and lower manufacturing cost.
Planar multiaxial fabrics having layers of parallel fibers at predetermined angles bound by a knitting process, known as non-crimp fabrics, are also commonly used in reinforced composites. Methods of making such planar multiaxial fabrics are disclosed in U.S. Pat. No. 4,518,640 to Wilkens. These methods are suitable for making flat fabrics with fixed width and yarn orientations. The in-plane layers normally include high performance fibers such as glass and/or graphite fibers, whereas the knitting yarns generally are made of flexible fibers such as poly(ethylene terephthalate) (PET) or aramid rather than using the same type of high performance fibers as in the in-plane layers.
Fabrics with solid rectangular or other cross sectional shapes such as I and T sections may be constructed with reinforcing fibers in both in-plane and through-the-thickness directions by three dimensional weaving and braiding processes, as disclosed in, for examples, U.S. Pat. No. 4,312,261 to Florentine and U.S. Pat. No. 5,085,252 to Mohamed et al. These processes are generally limited in the cross sectional shapes and dimensions of the fabrics that can be produced.
Fully interlocked and adjacent layer interlocked fabrics may be formed by weaving or braiding according to, for example, U.S. Pat. No. 4,174,739 to Rasero et al. In such fabrics the yarns are crimped due to yarn interlacing or intertwining, and the yarn crimps in the fabrics cause a reduction in the stiffness and strength of the composites reinforced with such fabrics. Although the fabrics layers are integrated by interlocking, there are no reinforcing yarns placed directly in the through-the-thickness direction.
Composite parts reinforced with hollow fabrics are widely used for many applications. Hollow fabrics such as tubular structures may be constructed directly from yarns, as disclosed in, for example, U.S. Pat. No. 4,001,478 to King, and U.S. Pat. No. 4,346,741 to Banos et al. and U.S. Pat. No. 6,129,122 to Bilisik. In all these disclosures, the yarns are primarily arranged in the axial, circumferential and radial directions, respectively. More particularly, the yarns in the axial direction are required as part of the fabrics structure, whereas the yarns in the circumferential direction at an angle close to 90° to the axis are placed into the fabric along a single direction only. These disclosures cannot afford hollow integrated multiaxial fabrics with yarns of the formed fabrics oriented in directions other than or in addition to the axial, circumferential and radial directions.
The traditional methods and machines of forming integrated fabrics lack in the flexibility of varying the fiber orientation, the cross sectional shape, dimension and are unable to provide hybrid structures of which the fiber architecture may change from location to locations as the fabrics are being formed, more specifically are unable to make hollow integrated multiaxial fabrics. They are often associated with other disadvantages such as low level of automation, low production rate, lack in flexibility and high manufacturing cost. And the traditional integrated hollow fabrics are not multiaxial structures for the lack of flexibility of varying the fiber orientations and forming hybrid structures of which the fiber architecture may vary from location to locations, among others.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.